SU1571527A1 - Apparatus for determining coefficient of nonlinear distortions of electrodynamic geophone with correction of error - Google Patents

Abstract

The invention relates to geophysical instrumentation and can be used in seismometry. The purpose of the invention is to improve the accuracy of determining the non-linear distortion factor of a seismic receiver. The device consists of a generator of sinusoidal oscillations, a current source controlled by a voltage, a reference resistor, a synchronous one-vibrator comparator, a notch filter, two end switches, a three-position switch, a quadratic voltage-frequency converter, and a frequency meter. The introduction of the closing key and the reference resistor, as well as the measurement sequence in three cycles, allow to compensate for the voltage drop on the active resistance of the seismic receiver when excited with a harmonic signal and free from instrumental errors of the measuring channel, which increases the accuracy of the non-linear distortion of the seismic receiver. 1 il.

Description

The invention relates to geophysical instrumentation and can be used in seismometry.

The purpose of the invention is to improve accuracy.

The drawing shows a block diagram of the device.

The device consists of a sinusoidal voltage generator 1, a comparator 2, a voltage-controlled current source 3, a reference resistor 4, a test receiver 5, a first closing switch 6 with one closing contact, a synchronous one-shot 7, a notch

the filter 8, the second closing key 9, the logic element 2I 10, the three-position switch 11 with the slots of the contacts 12, 13, 14, the frequency meter 15, the quadratic voltage-frequency converter 16.

The output of the generator 1 is connected to the inputs of the comparator 2 and the source 3 of the current controlled by the voltage. The output of comparator 2 is connected to a clock input of a synchronous one-shot 7, the control input of which is connected to the first contact of the key 6, and the second contact of this key is connected to a common point. First output synchronous

ate

el ee

sj

the one-shot 7 is connected to one of the inputs of the logic element 2I 10, the second input of which is connected to the output of the quadratic voltage-frequency converter 16. The output of the logic element 2И 10 is connected to the input of the frequency meter 15. The output of the current source 3 is connected to the position 12 of the three-position switch 11 and the first output of the reference resistor 4, the second output of which is connected to the position 13 of the three-position switch 11, the input of the notch filter, the first contact of the second closing switch 9 and the first output of the test seismic receiver 5. The second contact of the second closing key 9 and the second output of the tested seismic receiver 5 are connected to a common point. The output of the cut-off filter 8 is connected to the position 14 of a three-position switch 11, the common terminal of which is connected to the input of a quadratic voltage-frequency converter 16.

The device works as follows.

When direct current is applied to the geophone coil, the latter is a purely active resistance Rccush.

When a seismic receiver is excited by a harmonic current with a frequency equal to its own, it is, according to an equivalent circuit, a series-connected coil impedance and an active mechanical impedance of an equivalent replacement circuit. However, the impedance modulus (Zf) of the geophone coil can be replaced at its own frequency with sufficient accuracy by the active resistance value RK of the coil. Really

 f

R

 t h

+ W0 Lk,

(one)

where LK is the inductance of the coil, W0 cyclic natural frequency.

The seismic receiver is not a perfectly linear oscillatory system and has some non-linearity. Therefore, an equivalent replacement circuit must include not only linear elements (on a natural frequency

This is an active mechanical resistance R), which, naturally, does not lead to the appearance of nonlinear distortions, but also nonlinear resistance, which causes their presence. The latter can be represented in the general case.

P

in the form of the sum Z .. where Z- is non-

The part of the equivalent resistance of the seismic receiver that causes the appearance of the i-th harmonic in its output signal.

Then the nonlinear distortion coefficient KHVt of the seismic receiver can be written as

P

 | z,

R

(2)

0

five

0

five

0

five

0

five

The measurement process is carried out in four cycles, each of which begins on a short circuit in key 6.

The output voltage of the generator 1 is converted by the current source 3 into a harmonic current signal, which excites the test receiver 5. The output signal of the generator 1 is also fed to the input of the comparator 2, with which it is converted from a sinusoidal signal to the same-frequency clock signal to the synchronous one-frequency clock. 7. When the potential changes at the control input of the latter, which is achieved by a short-term closure of the key 6, at its exit there appear single gates, the duration of which is Atna period CHI- generator 1 "

In the first measurement cycle, the key 9 is open, and the switch 11 is in position 13, and the signal of the seismic receiver 5 is fed to the input of the quadratic converter 16. The first harmonic of this voltage is determined by the sum of the coil resistance RK and the equivalent resistance R of the seismic receiver and the higher harmonics - nonlinear part of the equivalent resistance of the seismic receiver. Therefore, after a short-term closure of the key 6, the output of the logic element 2I 10 appears a packet of pulses, quantities o n which according to function

square-to-voltage converter - the frequency will be equal to

owls, and

N4

N,

(7)

N, M „- K12 (IR + R) 1 + Ј Z-J (3) where N is the number of pulses at the output of a quadratic converter 16 voltage is the frequency when its input is closed to the common point} k is the conversion factor

quadratic converter,

I is the current of the source 3 of the voltage controlled current. Taking into account that the non-linear distortion factor of the seismic receiver is not more than 0.2%, the last term of the expression (3) can be neglected. Then expression (3) can be rewritten in the form:

N

f

N.

- kIZ (Rk + R)

In the second measurement cycle, the switch 9 is closed, and the switch 11 is switched to the position 12, and the voltage on the reference resistor R3T is applied to the input of the quadratic converter 16. After a brief closure of the key 6, a packet of N pulses appears at the output of the logic element 2I 10, moreover

N

Nn - kl R

. t

In the third measurement cycle, the key 9 is open, and the switch 11 is transferred to position 14, and the voltage-frequency comes from the output of the notch filter 8 to the input of the quadratic converter 16, the harmonics of the output signal of the seismic receiver 5 are short-circuited at the output of the logic element 2and 10 a bundle of Ns pulses appears, with

"3

N. - kl Z Z

In the last fourth measurement cycle, the key 9 is closed, and the switch 11 is switched to the position 13. And the input of the quadratic voltage converter 16 is the frequency connected to the common point. After pressing button 6, a packet of N pulses appears at the output of logic element 2И 10

In each measurement cycle, the number of pulses Nf - N4 in packs is calculated by a frequency meter 15 operating in the pulse counting mode.

From expressions (4), (5), (7), we find the equivalent resistance R - of a seismic receiver

R

- R

(eight)

D N4 N. R ET

From expressions (5), (6), (7),

I g 1 non-linear part X Z, equiv. 1 1

seismic tape resistance

25

(s;

V, from 7

N - Ne NA - N

eg

(9)

Nonlinear distortion factor. seismic receiver is determined by the ratio of expressions (9) and (8):

thirty

neither

(ten)

35

40

45

50

55

As follows from expression (10), the result of measuring the nonlinear distortion coefficient of a seismic receiver does not depend on the coefficients of the transformation function of the measuring channel.

Thus, the invention makes it possible to isolate its output signal directly from the total voltage on a seismic receiver, which makes it possible to correct the methodological error of measuring the nonlinear distortion coefficient at the natural collector frequency and thereby improve the accuracy of determining the nonlinear distortion factor of the seismic receiver.

Claims (1)

Invention Formula A device for determining the nonlinear distortion coefficient of an electrodynamic seismic receiver with error correction, containing a sinusoidal voltage generator, a voltage controlled current source, a notch filter, a three-position switch, a quadratic voltage-frequency converter, a comparator, a synchronous one-oscillator, the first closing key, a logic element 2I, the frequency meter, the input of the square-voltage converter - the frequency is connected to the common output of a three-position switch, its output is connected to the first input of logic element 2I, the second input of which is connected to the output of a synchronous one-oscillator, the clocking input of which is connected to the output of the comparator, and the control input to the first contact of the button, its second contact is connected to a common point, where the cud is also connected The first pin of the tested seismic receiver, the second pin of which is connected to the input of the notch filter, the output of which is connected to the first position of the three-position switch, the output of the sinusoidal voltage generator is connected to the com a parator and a current source controlled by a voltage, the output of logic element 2I is connected to the input of a frequency meter, distinguished by the fact that, in order to improve accuracy, it is equipped with a second closing key and a reference resistor, the first output of which is connected to the second a geophone, a notch filter input, a second position of a three-position switch and a first contact of the closing switch, the second contact of which is connected to a common point, and the second output of the reference resistor is connected to the output of the current source controlled by direct voltage and the third position of the three-position switch.